It is known that during the initial operation of a new or clean internal combustion engine, a gradual increase in octane requirement (OR), i.e, the fuel octane number required for knock-free operation, increases with the buildup of combustion chamber deposits until a stable level is reached which generally corresponds to a time when deposits remain relatively constant The actual stable level can vary with engine design and even with individual engines of the same design.
Many additives are known which can be added to hydrocarbon fuels to attempt to prevent or reduce deposit formation or remove or modify formed deposits in the combustion chamber and adjacent surfaces, such as valves, ports, and spark plugs, in order to reduce octane requirement.
Continued improvement in design of internal combustion engines, e.g., fuel injection and the like, brings changes to the atmosphere of the combustion chamber so there is a continuing need for new additives to control the problem of deposits and improve drivability which is usually related to deposits.